1. Field of the Invention
The present invention relates to driving circuits and methods for use with high voltage bidirectional semiconductor switches. In particular, the present invention provides for a driving circuit that utilizes a bootstrap capacitor and a driving circuit with self supply from a DC bus.
2. Related Art
Recently developed bidirectional III-nitride switches are particularly useful in the field of high power and high frequency electronics. A bidirectional III-nitride switch typically includes a substrate which may be composed of Si, SiC, Sapphire, or the like, a first semiconductor body formed over the substrate comprised of gallium Nitride (GaN), and a second semiconductor body formed over first semiconductor body and composed of AlGaN. The heterojunction of GaN and AlGaN produces a highly conductive two-dimensional electron gas (2DEG) at or near the heterojunction. The 2DEG is formed due to the spontaneous polarization effect as is known in the art. Two Ohmic power electrodes are ohmically connected to the second semiconductor body (AlGaN). Two gate electrodes may be positioned a predetermined distance from each of the two ohmic resistors. The bidirectional III-nitride switch described above is a depletion mode device in that it is normally ON. The application of an appropriate voltage to either of the gates, however, causes an interruption of the 2DEG which turns the switch OFF. Generally, the voltage that is applied to the gate or gates to turn the switch OFF is a voltage that is more negative than the potential at either of the ohmic electrodes. Additional and non-limiting examples of bidirectional switches can be found in U.S. Patent Publication No. 2005/0189561 entitled III-NITRIDE BIDIRECTIONAL SWITCH, filed on Feb. 11, 2005 in the names of Daniel M. Kinzer and Robert Beach and assigned to the assigned of the present application, the contents of which are hereby incorporated by reference.
The bidirectional switches discussed above are particularly useful for use in high voltage, high frequency systems and as such are useful for most any power electronics application over a wide range of topologies.
However, given the somewhat unique characteristics of these switches as depletion mode devices, it is desirable to provide improved driving circuits and methods to control these switches.